The published Bazaar branches include 8 years of history going back to MySQL 3.23.22, imported from the BitKeeper repositories. So you can see a lot more than just the history since the switch: you can use all the normal Bazaar tools to see where the code came from and how it evolved. Giuseppe Maxia has posted some instructions on how to check out the code for those who are interested.
I haven’t checked extensively, but I wouldn’t be surprised if this is the largest public code base managed with Bazaar. I’ve known from personal experience working on Launchpad that it is capable of handling large trees, but it is good to have a high profile project to point at as an example now.